Electrical musical instrument



1951 L. E. A. BOURN ELECTRICAL MUSICAL INSTRUMENT 2 Sl-lEETSSl'lEET 1 Filed Aug. 7, 1947 L. E. A. BOURN ELECTRICAL MUSICAL INSTRUMENT 2 SHEETSSHEET 2 lll't Dec. 18, 1951 Filed Aug. 7, 1947 Patented Dec. 18, 1951 UNITED STATES ELECTRICAL MUSICAL INSTRUMENT Leslie Edwin Alexander Application August 7. In Great Britain Bourn, Ashford, England 1947, Serial No. 767,203 November 22, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires November 22, 1964 9 Claims. 1

This invention relates to electrical musical instruments oi the kind comprising a multiplicity of individual frequency generators which are brought into operation selectively say by the actuation of stops and keys. The invention is especially but not exclusively applicable to electrical musical instruments of the electrostatic type, an example of which is described in U. S.

Patents, Reissue #19,702 and ii-2,932,044.

In all the previous examples of musical instruments of the electrostatic type, the outputs from. all the frequency generators have been paralleled together and connected to a common output amplifier. Thus the output voltages from any one or more of the total number of generators is considerably reduced by virtue of the shunting efiect of the total capacity of all the remaining generators not in use. In certain cases, in which resistances are used to feed the polarising potentials to the respective generators, this deleterious shunting effect is still greater owing to the total number of resistances also shunting the output. Consequently, in previous musical instruments of the electrostatic type, the electrical response is small and high voltage polarizing is necessary. Also the signal/noise ratio is low.

of will now be described, reference being made to the accompanying drawings, wherein:

Figure 1 is a circuit diagram illustrating the essential circuits of a small organ in accordance with the invention;

Figure 2 is a circuit diagram illustrating an addition which may be incorporated in the arrangement of Figure 1;

Figure 3 is a circuit diagram illustrating the essential circuits of another small organ in ac-' cordance with the invention.

Referring first to Figure l, the organ to which this figure relates comprises two manuals and pedals with thirty-six speaking stops derived from four ranks of tone families and two expression or swell pedals.

The tonal scheme of this organ is set out in the following Table I which gives the ranks and the manner in which they are distributed on O the manual and pedal departments. It will be seen for example that Table I indicates that a rank, or set, of ninety-six generator elements, all of flute tone, are playable in three different pitches on the Swell, six on the Great and five on the Pedal. The pitches are given in foot lengths in order to comply with standard nomenclature:

Table I No.01 Lowest Rank Notes Note Swell (it) Great (ft.) Pedal (ft.)

Flute 96 000.. 16, 8,4 16, s, 4, 2%, 2, 1%.- 16 1034,, 8, 5%, Diapason 84 oo 3 8,4,2%,2,1 ,-,1. s.

ring 84 CG 8,4,2%,2,1 ,1 Reed 84 000.. 16, 3,4 8 16,8.

The present invention has for its object the provision of an improved electrical musical instrument in which, inter alia, this deleterious shunting eiTect in the case of instruments of the electrostatic type will be very much reduced.

A further object of ths invention is the provision of an improved electrical musical instrument having a new and simplified system of connections.

The invention consists broadly in the arrangement that the generators feed the output through the medium of electronic valves. The valves may be arranged so that each one amplifies the output of a single individual generator, or several of the individual generators may be paralleled through a single valve. The outputs from the valves may be applied to an output amplifier and this supplies a loud speaker or loud speakers.

In order that the invention may be the more clearly understood, certain embodiments there- The following Table II gives the stop names allocated to the various pitches in the order in which they appear in Table I:

Rank Stop Name Pitch Remarks GREAT Flute Double Flute Flute 8 Flute 8 it. mi. Clarinet (synthetic). Flute Twelfth f.

l Tierce p. Open Diapason. Dulciana 8 Open Dia. pp. Principal I Dulcet Principal pp. Twelfth Fifteenth 2 it Twelfth pp. Mixture IV Ranks.. Ffteenth PDD. DPPP- Trumpet 8 it PEDAL Flute Bourdou Do Acoustic Bass 32 it.. ft Bmlrdon Do Do Diapason-.-

ecd Do To carry the above requirements into effect, a set of twelve generator structures l is required, only three of which are shown in the drawing. Each of these structures comprises a stationary disc 2 and a coaxial adjacent rotating disc 3. Much in the manner described in my prior Patent,#2,032,044, each stationary disc 2 is engraved with coaxial rings 4 which are given wave forms and each rotating disc 3 is engraved with a grid which is adapted to scan the wave formed rings of the adjacent stationary disc. Unlike the arrangement described in patent #2,032,0e4, however, the wave forms of the rings 4 instead of being sinusoidal, correspond to the wave forms of the complete flute, diapason, string and reed tones. Thus, the twelve discs being engraved with wave forms for all the notes of the said four ranks, a total number of 348 rings 4, i. e. 29 per disc will be required. The scanning grids on the rotating discs 3 are connected to a source of polarization supply 5 of any suitable voltage. Owing to the increased efliciency which thepresent circuit provides, this voltage need only be of the order of, say, twenty volts.

The wave-forms engraved upon the discs and which form the generator elements may be derived by photographic methods directly from an oscillograph trace of the actual tone required.

All the twelve structures I are identical both electrically and mechanically, but their discs 3 are driven at different speeds such that the twelve semi tones of the octave are produced. The lowest speed is 978.75 revs. per minute and, at this speed, a ring 4 having two complete waves per circle will produce 16 it. C (ccc) at 32,625 c/c. Thus, according to Table I each disc 2 will be engraved with two rings each having two complete waves per circle, one of flute tone and the other of reed tone, and these rings in all will produce the bottom octave of those two ranks. For the next octave, rings with four waves per circle will be required,'and each disc 2 will be engraved with four of such rings, two to continue the ranks already started and two to commence the diapason and string tone ranks. These are followed by four rings each of eight waves per circle and so on until all the ranks are complete. Although not in accordance with Table I it may be desirable to represent the mutation pitches such as 2 feet, 1% feet etc., at the true harmonic frequencies, and not to borrow them I from the musical scale.

Each individual ring 4 is connected, through a variable condenser 6, to the control grid of an electronic valve I. By variation of the condenser 6, the strength of the input signal to the grid of the valve 1 may be varied. Each valve I has a resistance 8 in its cathode circuit for the purpose of producing negative current feed back, which stabilises the performance of the valve and also modifies the grid bias/gain characteristic. The value of these resistances is adjusted in order to make this characteristic uniform for all the valves. 7

The anodes of the valves are connected to-' gether in groups and those of each group are connected, through an anode resistance 9, which is common to that group, to a suitable plate current source. It is convenient to form two of such groups, one including all frequencies up to about 200 c./s. and the other all frequencies above 200 c./s. The value of each resistance 9 must be low compared with the slope resistance of the valves in order to minimise intermodulation when a number of notes are sounding together. Each group is connected through a condenser Hi to an output amplifier H and thence to the loud speakers l2.

The control grids of the valves fl are normally kept at a negative potential equal to, or just in excess of, the cut-off value, by means of a source of potential l3. This source communicates with each grid by way of resistances l4, l5 and [6 which are proper to that grid. Resistance [6 is a normal grid resistance and may be of the order of two megohms. A condenser I1 is connected across resistances f4 and I5, and resistance l5, in conjunction with said condenser l1, acts as a low pass filter. Further mention of this network will be made hereinafter. Resistance I4 is normally of the order of 1000 ohms, and its junction point l8 with resistance [5 is connected to all points in the keying system which require that particular tone, as will appear hereinafter. Thus, normally, although signals are being continuously applied to the control grid of the valve 1 from the appropriate element 4, no signal is relayed through the valve.

Describing now the key and stop circuits, each key-board has associated therewith a number of horizontal bus bars I9, corresponding to the pitches shown in Table I, and each key of that key-board has associated therewith a vertical trace 2B bearing a number of contacts 2|, the arrangement being such that, upon the actuation of any key, the corresponding trace 2B is moved vertically so that all the contacts 2! appertaining to that key are connected respectively to the bus bars [9. The key contacts 2| are connected to the appropriate points l8, and the bus bars iii are energised according to the actuation of the stops as will hereinafter appear.

It will be seen that there are, in the instrument being described, three distinct sets of bus bars I9, corresponding to the three keyboards. In Figure 1 only the first three bus bars of the swell manual are shown, which, it will be seen from Table I, correspond to the 16, 8 and 4 foot pitches of the flute rank. The valve I, which is illustrated, is shown cross-connected from its junction point iii to the second C on the 16 foot but bar l9 and to the first C on the Bi'oot bus bar I9. Consequently, the tone to which this'particular valve corresponds is the 13th note of the flute rank corresponding in pitch to 8 footC (cc). The method of cross connecting the mutation pitches such as 2% ft., 1% it, -'etc., will be obvious to those skilled in the'art. The traces 29 are normally operated by means of respective electromagnets, a single contact appertaining to each key closing when said key is actuated and energising the respective magnet which thereupon lifts the trace and engages all the key contacts 2| for that key with the respective bus bars |-9. The various intermanual couplers form part of these action circuits and require no description.

The references 22 and 23 designate conductors leading from the same point |-8 to the other two keyboards.

The connection from each key contact 2| to its'point |6 is by way of a resistance 24 and recti-fier 25 in series as shown. The value of the resistance 24 is normally of the same order as that of the resistance l4, viz. I000 ohms, and, owing to the low order of voltage necessary for the operation of these circuits, a single disc rectifier will. 'siiflice for each rectifier 25. I

The bus bars l9 are supplied from a source of potential 21. Each bus bar is connected through a resistance 28, of value low compared to that of the key resistances 24, to the negative side of saidsource 21, and the energisation of said bus bars is effected from a common slider 29 which slides on a potentiometer resistance 3|) connected across said source 21, said slider being adapted to be connected through respective resistances 3! and stop operated contacts 32 to th respective bus bars. The contacts 32 are brought into engagement with their bus bars according to the operation of the stops, and it will be seen that. whereas normally the bus bars are maintained at zero potential by means of the resistances 28. each time a contact 32 engages a bus bar is raised to a given potential depending on the resistance values. The position of the slider 29 and therefore the potential to which the bus bars I!) are raised, is controlled by means of a swell'pedal 533.

The reference 34 denotes a second and similar potentiometer resistance, connected across the source 21, whose slider 35 i controlled by means of a similar swell pedal. This slider 35 feeds the bus bars of both the Great and the Pedal departments so that volume expression of both of these departments is under control by the same pedal. Alternatively, of course, each of these departments could have a potentiometer, sheer and swell pedal to itself.

It will be understood that if, by way of example, the Lieblich Bourdon stop be drawn, the appropriate contact 32 will close on the upper blls bar illustrated, and current will flow to said bus bar which will accordingly be raised to a potential value as determined by the setting of the swell pedal slider 29 and also bythe value of the stop feed resistance 3|. These resistances 3| are incorporated in order that the potential values and hence the loudness at which the stops will sound may be preset. They may, however, be omitted altogether if the maximum loudness is required for any particular stop. It is, however, generally desirable carefully to set the levels of the different stops in order to obtain a satisfactory tonal "tout ensembleand balance. If now the key C2 is operated, all the key contacts 2| appertaining thereto will close on all the I the softer stops.

bus bars |-9, but as, at the moment, only the upper bus bar is energised, only the single corresponding note will-sound, as current will flow from only the energised bus bar through key contact 25, resistance 24 and rectifier 25, and through resistance l4 across which will appear a potential which is communicated to the control grid of the valve 1. Thus the bias on the said control grid, which normally prevents any signal from being passed on to the loud speakers, is reduced so that the vibrations generated by the corre sponding ring 4 are relayed through the valve and transmitted to the loud speakers. It will be seen that the intensity or volume of the sound produced will be a function of the amount to which the bias has been reduced. It will also be appreciated that, whereas, in previous electrostatic instruments, control voltages of the order of hundreds were necessary, voltages of the order of about six volts are suificient for controlling the grids in the present arrangement.

If now .ke'y C! be operated as well as key C2, the bottom C of the rank will also sound through. the appropriate contact, resistance, rectifier and valve. It will be noted that as all contacts on both keys C| and C2 are now closed, the poten tial existing on the illustrated junction point i8 resulting from the operation of the key C2 will tend to flow to the second bus bar l9 (Gedackt) which is at zero potential, as its stop has not been drawn. The presence of the rectifier 20, however, effectively prevents this and the defect of robbing accordingly does not take place.

If now, whilst the two keys Ci and C2 are in operation, the Gedackt stop is drawn, thus energising the second bus bar is, provided that the potential to which it is raised is greater than A that of the upper bus bar, additional current will flow through the resistance id and the particular note will sound at a lender level which, owing to the grid bias/gain characteristic of the valve, will be substantially in accordance with the expected increment caused by the two notes of two stops of equal pitch being sounded together.

It will be noticed from Table II that on the Swell, the String Rank draws twice at 8 ft. pitch under the names of Gamba and Salicional, similarly also on the Great the Diapason draws under the names of Open Diapason and Dulciana. In these cases, the Salicio'nal and Dulcianais a softer rendering of the Gamba and Open Diapason, hence it is possible to use the same bus bar for both in each case, the only difference being that a greater value of stop feed resistance is used for The employment of the same stop sounding at different strengths is known as double winding the name being taken from the practice of sounding organ pipes on lower wind pressures.

It will be further noticed that on both manuals, stops appear under the name of Mixture IV Ranks. Such stops are well known to organ builders and are used to enhance the tonal blend of the instrument. This is a case of doublewinding where bus bars of the requisite pitches al ready exist, but if not additional bus bars must be added where necessary. Each stop in these cases cited operates four separate contacts 32 each associated with the aprc-priate bus bars.

On the Great, it will be seen that a synthetic Clarinet stop has been included. This is yet another instan'ceof double winding and in which a new known tone may be produced from a combination of existing tones. It is obvious that any such combinations may be employed for the pro- I each set of discs.

7 duction of a'ver'y large variety of 'newand novel effects.

As was mentioned earlier, a low-pass filterin each grid bias feed is incorporated consisting of resistance 15 and condenser IT. The function of these circuits is to assimilate as nearly as possible the tonal build-up or attack of an organ pipe. It will be seen that as the potential is suddently applied at the point 18, the potential rise is gradual across the condenser H, as is also the potential applied to the valve. Such a circuit is essential for the avoidance of key clicks." The component values are graded throughout the musical compass so that the trebles are prompter in speech than the basses; the reed is made prompter than, say, the string.

The tones maybe made todie'away more gradually by theincorporation of an additional condenser 36 and a rectifier 31 shunted by a resistance 38 as shown in Figure 2. Thus the rectifier 31 is connected between the point l8 and the re-' sistance l5, and the condenser 36 is connected between the junction point of the rectifier 3'! and the resistance l and the positive terminal of the source 13. It will be seen that the rectifier 31 will allowthe condenser '36 to charge rapidly and to slowly leak away through the resistance 38.

In the instrument described, all tone ranks are represented by elements 4 mounted upon the same set of generator discs. In more advanced instruments, it may be beneficial to provide a separate set of discs'for each rank, the associated valves 1 being connected so that their outputs feed into amplifiers and loudspeakers individual to Each rank will then have an entirely independent output'and also an independent origin. As the discs are usually belt driven, there will exist slight differences of pitch and steadiness. Such differences, if not too great, are of considerable importance to the overall effect, as each separate tone then sounds as an independent instrument and stands apart from the other tones. This is not the case when all frequencies are locked together with mechanical precision as is the case when all tones are derived from the one set of discs.

In the embodiment just described with reference to Figures 1 and 2 each individual element 4 has its own proper associated valve 1, and thus any shunting load due to the inoperative generator elements is prevented. As even the smallest instrument entails the use of approximately one hundred generator elements, it may be stated approximately that the output of a single generator element would be reduced to /100 by the shunting effect of the remaining elements. Obviously the shunting effect can be in a considerable measure reduced, although not so fully as in the embodiment above described, if each valve is associated with a group of generator elements instead of with one individual generator element. Such an arrangement is illustrated in Figure 3, which has the additional advantage of a new and simplified system of connections.

This" figure illustrates an instrument which may be of the same general type and tonal scheme as that of Figure 1. Its'principal difference from the instrument of Figure 1 is, firstly, that, instead of having twelve generator structures i corresponding to the twelve semi tones of the octave, it has a generator structure I for each key of the instrument and a valve 1 for each generator structure. The wave forms of the rings 4 on each stationary disc 2, and the speed of rotation of the corresponding rotating disc 3 are such that said rings 4 are adapted to produce all the frequencies, whether they are pure or complex, which are required by that particular key.

Although, by such an arrangement, the maximum eificiency is not attained, certain other ad-' vantages are gained, for example, for a two manual instrument with pedals, a total of 154 valves are required, compared with the 348 required by the arrangement of Figure 1. Also the number of contacts operated by a single key is reduced to a single contact, other contact only being necessary for couplers. It will be appreciated that the number of generator structures could, if desired, be reduced to one half by employing two stationary discs 2 in each structure; one each side of'a single rotating disc 3, which would bear a scanning electrode on each face.

Although the principle embodied in Figure 3 lends itself perfectly to the use of rings 5 adapted to generate complex tones as in the case of Figure 1, the rings 4 in the actual arrangement to be described generate pure tones and the tone are mixed by circuit control. It is assumed that there are ten harmonic frequencies per key, or, in other words, that each stationary disc 2 bears ten rings 4, adapted to generate the said ten harmonic frequencies. It may be noted in passing that, with this arrangement, the voltage generated by a single element 4 will-be reduced to approximately one tenth owing to the shunting effect of the remaining 9 elements 4 on the same disc 2 and associated with the same valve 1. This, however, represents a considerably higher efilciency than has been obtained by previous systems- The precise number of stops or tonal varieties which could be obtained with the above number of harmonics is theoretically large, but, with o small a complement of harmonics, the practicable number would probably be about twelve. The frequencies per note in the example bein described are as follows: In foot pitches they are 16, 8, 5%, 4, 2%, 2, 1%, 1 1 and 1. These correspond to harmonics 1, 2, 3, 4 at 16 ft. pitch, 1 to 8 at 8 ft. pitch, 1 to 4 at 4 ft. pitch and 1 and 2 at 2 ft. pitch. Table III gives the number of waves per circle of the elements 4 on the diiierent discs 2, and the speeds at which they are run for the manuals. For the pedals, the same discs are used as for the first 32 notes of the manuals. a

In the circuit ofFigure 3 only three generator structures v I are shown. The scanning grids which are engraved on the rotating discs 3 are each connected, through a variable condenser 6, to the control grid of a valve 1. The anodes of the valves 1 are paralleled as in Figure 1 and the manner in which they are fed and in which the outputs are supplied to the loud speakers is the same as in Figure 1 as will be seen from the same references which are applied to like parts in the two figures. Also, the network by which the control grids of the valves 1 are normally kept at a potential equal to, or just in excess of, the cut-off value,'by means of a source of potential i3, is the same as in Figure l as will be seen by the references. In the present case, the resistance l4 may be of any convenient value as it serves only to hold the grid at the cut-off value from the source i3.

Also as in Figure 1, a source of potential 23 is provided, having potentiometer resistances 3d and 3-1 connected thereacross, said potentiometers being provided with slidersze and 35, actuated by swell pedals, for feeding the different departments. In the present-case, however, said sliders do not supply the bus bars Iii, but each one supplies a bus bar 39, which is common to all the keys 40 of that department. As will be seen from the drawings, when any key til is depressed, the bus bar 39 is connected through a contact ti with the point is appertaining to that particular key.

The elements 4 corresponding to 16 ft. pitch on all the discs 2 are connected together throughout the entire compass of the manual (or other department) by a common lead 2, and likewise the 8 ft., 5 ft. elements and so on. These leads 42 are respectively connected to the bus bars IS. The bus bars iii in the present case are adapted to be polarised by a source of potential as and are normally maintained at zero potential by being connected through resistances 28 to the negative side of said source. In the present case, these resistances 23 may be of the order of 01 megohm.

Each step has an associated trace i i and said trace carries contacts at which are connected through respective stop-feed resistances fifi'to the positive of the source as, and when the stop is "drawnthe trace is moved so as to bring its contacts 35' into engagement with the appropriate bus-bars 19. Each stop will, of course, close contacts as on to the bus bars corresponding to the harmonics in the required tone, and the resistances 46 are, of course, chosen so as to provide the required harmonic strengths.

It will now be seen that, if a key Calls depressed, current will flow through the resistance M corresponding to said key, and the junction point l8 will be raised to a potential determined by the setting of the slider 29 operated by the swell pedal. The corresponding valve 7 will accordingly be restored to its amplifying condition, but, if no stop is drawn, theelements 4 associated with said valve will be at zero potential and no sound will result.

If now a 16 ft. flute stop is drawn requiring only the single harmonic, a contact will close only on the 16 ft. bus bar i9 and this will cause all the 16 ft. elements 4 throughout the whole compass to become polarised, but as all the valves 1 except that corresponding to the depressed key are non-transmissive the 16 it. harmonic will sound only in the case of the note represented by that stop. In like manner, if a stop is drawn requiring a number of harmonics, the corresponding bus bars 19 will be polarised, and, when a key is depressed, those harmonics will sound on the note corresponding to that key.

If two stops be drawn together, both of which involve the polarisation of the same bus bar, say the 16 ft. bus bar, this bus bar will be polarised to a higher potential owing to the two resistances 46 in parallel. Thus, the correct additive efiect will be obtained.

A tremulant of the amplitude modulation type may be put into effect by modulating the potential applied to either the second or third grids of the valves 1 (which are shown as pentodes) by means of an electronic oscillator. A frequency modulation tremulant may be provided byoscillating the normally stationary discs 2 in the manner described in British Patent No. 448,193.

An instrument with a separate disc structure per key as in Figure 3 may-be used to form what is known as a Celeste. This is a second tone usually of a: string-y nature which is nearly but not quite in tune with the remainder of the tones. Thus, when this is played in combination with other stops a slow beating takes place. In order that such an effect shall be artistic, the speeds must be carefully graded throughout the compass. This can only-'be'accomplished wherebelt drive for the discs 3. is used, in which case, by means of adjustable pulleys, the beats may be graded throughout the compass. These additional discs for the Celeste are connected so that the rotors 3 are-parallel to the appropriategrids of valves already in use. The elements are joined as before but to form a separate set of bus bars and stops. It is usually-more economical to employ a single set of complex waves which are energized at will by a single stop.

In order toreduce substantially the number of discs in the arrangement of Figure 3, this may be modified in such a way that all the Us are arranged on asingle disc and likewise all the Cits, Ds, etc; The number of valves will still be the same as the number of keys and there will thus beseveral-keysand valves per disc.

This may be done by connecting the scanning grids so that they-are maintained at zeropotential with regard to-thenegative end of the source 3. The elements 4 pertaining to thesamekey would be eachconnected through a condenser to the grid of the pertaining valve i. The'junctions between the said element 4- and the said condensers'would be each connected through a high value resistance to the appropriate leads Band thenceto the bus bars l9.

This last named embodiment is, however, less efilcient electrically than that of Figure 3 owing to the additional shunt resistive load imposed across the output'due to the-presence of the resistances.

We claim:

1. An electricalmusicalinstrument comprising loud speaker means, a multiplicity of frequency generators, said generators including electrodes between which the frequencies are generated in the form of undulating potential differences induced electrostatically, electronic valves through which said frequencies are transmitted to said loud speaker means, said electronic valves each having a control electrode, means whereby the control electrodes of, said valves are normally kept at a negative potentialfor rendering, said valves non-transmissive, said last named means comprising a source of negative potential, three resistances in series between each control electrode and said source, and a condenser connected across twooisaid resistances, and control means for selectivelyraising thepotentials of said control electrodes andthereby rendering said valves selectively transmissive, said control means comprising a source of positive potential and means for selectively connecting the points between those pairs of resistances across which the condensers are connected to said source of positive potential.

2. An electrical musical instrument comprising loud speaker means, a multiplicity of frequency generators, said generators including electrodes between which the frequencies are generated in the form of undulating potential differ- 'cnces induced electrostatically, electronic valves .through which said frequencies are transmitted ,tov said loud speaker means, a resistance in the cathode circuit of each valve for the purpose of 3 producing negative current feed back, the values of all the cathode circuit resistances of all the ,,valves being adjusted to make the grid bias gain characteristic substantially uniform for all the valves, and control means for rendering said elecg tronic valves selectively transmissive.

3. An electrical musical instrument comprising loud speaker means, amultiplicity of frequency generators, said generators being arranged in groups, those of each group corresponding to the partials of one respective note only, a common output from the generators of each group to said loud speaker means, which output is individual to that group only, and means for controlling said common output.

, 4. An electrical musical instrument compris ing loud speaker means, a multiplicity of frequency generators, said generators being arranged in groups, those of each group corresponding to the partials of one respective note only, a common output from the generators of each group to said loudspeaker means, which output is individual ,to that group only, stops for controlling the energization of said generators, and keys for respectively controlling said commonoutputs, each key being individual to each common output.

, 5. An electrical musical instrument comprising loud speaker means, a multiplicity of frequency generators, said generators being arranged -in groups, those of each group corresponding to the partials of one respective note only, a common output from the generators of each group to said loud speaker means, which 1 output is individual to that group only, stops for controlling the energization of said generators, electronic valves connected in said common outputs, each electronic valve being individual to each common output, and keys for controlling said electronic valves and thereby respectively controlling said common outputs.

6. An electrical musical instrument comprising loud speaker means, a multiplicity of frequency generators,. said generators including electrodes betweenwhich the frequencies are generated in the form of undulating potential difierences induced electrostatically, said generators being arranged in groups, those of each group corresponding to the partialsof one respective note only, each group comprising a plu- 'rality of individual electrodes and a common scanning electrode which is individual to that group only, a common output from the generators of eachgroup to said loud speaker means which generated in the form of undulating potential differences induced electrostatically, said generators being arranged in groups, those of each group corresponding to the partials of one respective note only, each group comprising a plurality of individual electrodes and a common scanning electrode which is individual to that group only, a common output from the generators of each group to said loud speaker means which output is individual to that group only and is taken from said common scanning electrode, stops for controlling the energization of said individual electrodes, and keys for respectively controlling the common outputs.

8. An electrical musical instrument comprising loud speaker means, a multiplicity of frequency generators, said generators including electrodes between which the frequencies are generated in the form of undulating potential differences induced electrostatically, said generators being arranged in groups, those of each group corresponding to the partials of one respective note only, each group comprising a plurality of individual electrodes and a common scanning electrode which is individual to that group only, a common output from the generators of each group to said loud speaker means which output is individual to that group only and is taken from said common scanning electrode, stops for controlling the energization of said individual electrodes, electronic valves connected in said common outputs, and keys for controlling said electronic valves and thereby respectively controlling said common outputs.

9. An electrical musical instrument comprising loud speaker means, a. multiplicity of frequency generators, said generators including electrodes between which the frequencies are generated in the form of undulating potentials induced electrostatically, electronic valves through which said frequencies are transmitted to said loud speaker means, said electronic valves being individual to said generators each to each, means for permanently energising said generators, bus bars, stops for selectively polarizing said bus bars, and keys for selectively connecting said valves to said bus bars for rendering said valves selectively transmissive.

LESLIE EDWIN ALEXANDER BOURN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 7 Name Date Re. 19,702 Bourn Sept. 17, 1935 Re. 21,554 1 Curtis Sept. 10, 1940 2,126,464 Hammond Aug. 9, 1938 2,237,105 Miessner Apr. 1, 1941 2,276,390 I-Ianert Mar. 17, 1942 FOREIGN PATENTS Number Country Date 501,520 Great Britain Feb. 28, 1939 

